Injection molding provides a convenient way for preparing various articles from thermoplastic resins, particularly objects of a relatively intricate nature. In order to injection mold articles in an economic manner, it is important to minimize the adhesion of the molded part to the mold surface through the use of a release agent. It is additionally advantageous that the release agent be incorporated in the material to be demolded. However, such an internal agent must be compatible with the resin, that is, it should not lead to any significant loss of the other physical properties such as transparency and melt stability as measured by the usual characteristics of the resin under normal conditions and heat treatments.
Of the thermoplastic resins which find a mold release agent useful from time to time are polycarbonate, copolyestercarbonate and blends of these resins with aliphatic polyester resins. As a result of the generally high temperature which these thermoplastics are subjected to during molding and the inherent sensitivity of these resins to chemical attack and degradation by additives which are often compatible with many other thermal plastics, it is necessary to select mold release agents with high temperature stability and compatibility with polycarbonates. Mineral oils are one types of mold release agents as described in K53,22556; K79,16559; K72,41093; K80,84353 and GB 2,077,742. Mineral oils are naturally occuring complex mixtures of paraffinic and naphthalenic hydrocarbons that are obtained from petroleum.
We have found that synthetic mineral oils derived from the oligomerization of alpha olefins followed by hydrogenation to remove unsaturation provide a surprising benefit over normal paraffins and conventional mineral oils as mold release agents in various polymers including polycarbonate, copolyestercarbonate and blends of polycarbonate with other resins including cycloaliphatic or aliphatic-cycloaliphatic polyester resins without introducing significant detrimental effects on color, stability and other properties associated with these resins.